As described in PTL 1, a method of performing electrolysis in two stages of performing electrolysis on a copper sulfate aqueous solution; and performing electrolysis again on a copper nitrate aqueous solution at a low current density of 100 A/m2 or less by means of using copper deposited on a cathode as an anode, is known as a method of producing high-purity copper.
Further, as described in PTL 2, a method of producing electrolytic copper foil in which mechanical characteristics and adhesion to a cathode are improved by combining a polyoxyethylene-based surfactant such as polyethylene glycol (PEG) with a copper sulfate electrolyte that contains chlorine ions, glue, and an active sulfur component, is known. Further, as described in PTL 3, a method of producing high-purity electrolytic copper in which the surface of copper is smooth and the amount of impurities such as silver and sulfur is small by combining a smoothing agent such as polyvinyl alcohol (PVA) with a slime accelerator such as PEG, is known.